client.c: Changed Agent Version method code for the check_version() call

The Agent Version method related code calls the check_version(), improving
modularization.

Removed versionFromServer variable from main(). It is only used in
check_version().

Signed-off-by: ERIK ALEXANDRE PUCCI <eap08@c3sl.ufpr.br>
Acked-by: Bruno Ribas <ribas@c3sl.ufpr.br>
Acked-by: Josiney de Souza <josineys@c3sl.ufpr.br>
Signed-off-by: Danilo K. S. Yorinori <danilok@c3sl.ufpr.br>